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Tropical Storm Grace Forecast Discussion Number 17
2021-08-17 16:53:03| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Tue Aug 17 2021 000 WTNT42 KNHC 171452 TCDAT2 Tropical Storm Grace Discussion Number 17 NWS National Hurricane Center Miami FL AL072021 1100 AM EDT Tue Aug 17 2021 The cloud pattern of Grace is gradually becoming better organized on satellite images, but the system still lacks distinct banding features over the eastern semicircle. Cirrus-level outflow from the system appears to be well defined. Flight-level and SFMR-observed surface winds, as well as dropsonde measurements, support an intensity of 45 kt for this advisory. Not much change in intensity is likely through this afternoon while the circulation of Grace interacts with the island of Jamaica. Thereafter, since the cyclone will be over the very high heat content waters of the northwestern Caribbean Sea with modestly low vertical shear tonight and Wednesday, strengthening is anticipated. Grace will likely become a hurricane tomorrow and continue to intensify before moving over the Yucatan Peninsula. The interaction with that land mass is expected to temporarily interrupt strengthening, with some reintensification over the Bay of Campeche in 3-4 days. The official intensity forecast is near the model consensus for the first half of the forecast period, but below the consensus for the latter part of the period owing to the inherent uncertainties for that extended time frame. Grace continues to move just a little north of due west, or at about 280/13 kt. A well-defined 500 mb ridge should remain entrenched to the north of the tropical cyclone for the next several days. Therefore, a continued west to west-northwestward track is likely to continue for most, if not all, of the forecast period. The official forecast is close to the previous one through 72 hours and just slightly south of it at 4-5 days. This is very similar to the latest multi-model consensus prediction. Key Messages: 1. Heavy rainfall across Haiti, Cuba, Jamaica, the Cayman Islands, and the northern Yucatan Peninsula may lead to flash, urban, and small stream flooding, with the potential for mudslides highest in Haiti and Jamaica. 2. Tropical storm conditions are expected over portions of Jamaica today, and over the Cayman Islands later today and tonight. Tropical storm conditions are expected over portions of the southern coast of Cuba today in the warning area, spreading westward to possibly other portions of the southern coast of Cuba this evening through Wednesday morning. 3. There is an increasing risk of wind, rainfall, and storm surge impacts on the Yucatan Peninsula of Mexico Wednesday night and Thursday, and a Hurricane Warning will likely be needed for that area later today. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 18.3N 76.8W 45 KT 50 MPH 12H 18/0000Z 18.8N 79.0W 55 KT 65 MPH 24H 18/1200Z 19.2N 82.2W 65 KT 75 MPH 36H 19/0000Z 19.7N 85.3W 70 KT 80 MPH 48H 19/1200Z 20.4N 88.3W 65 KT 75 MPH...INLAND 60H 20/0000Z 20.9N 91.3W 60 KT 70 MPH...OVER WATER 72H 20/1200Z 21.1N 94.0W 65 KT 75 MPH 96H 21/1200Z 21.5N 98.5W 65 KT 75 MPH...INLAND 120H 22/1200Z 21.5N 103.0W 30 KT 35 MPH...POST-TROP/INLAND $$ Forecaster Pasch
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